Re: [PATCH v4 0/3] crypto: skcipher - per-request multi-data-unit batching

[Eric Biggers <ebiggers@kernel.org>]

On Tue, Jun 16, 2026 at 12:13:03PM +0800, Herbert Xu wrote:
> On Mon, Jun 15, 2026 at 03:53:17PM -0700, Eric Biggers wrote:
> >
> > So in other words, this series slows down dm-crypt and crypto_skcipher
> > for everyone to optimize for an out-of-tree driver.  And there's also no
> > benchmark showing that your driver is even worth it over just using the
> > CPU.
> 
> There is no reason why the software fallback should be slower
> than the status quo.  Existing callers of the Crypto API will
> be issuing one indirect function call per data unit.  With the
> new scheme, the indirect calls per unit moves from from the caller
> into the Crypto API.

Have you checked the code?  This patchset adds overhead in multiple
places.  Dynamically allocating multiple scatterlists and then parsing
them, adding a new field to skcipher_request for everyone, new checks in
crypto_skcipher_en/decrypt for everyone, new checks to validate the data
unit size that the caller knew was valid in the first place, etc.

> In fact, we could move it down further and improve upon the
> status quo by splitting the data in each algorithm implemntation
> so that the calls per unit become direct function calls and only
> the overall call into the Crypto API remains indirect.

That's not what this patchset does.  But also, as we know, a better way
to eliminate "Crypto API" overhead is to call the algorithms directly.

- Eric